Security systems are generally known. Such system typically include a number of sensors that detect security threats associated a secured area. The security threats may include those posed by intruders or by environmental threats such as fire, smoke or natural gas.
Included around the secured area may be a physical barrier (e.g., wall, fence, etc.) that prevents intruders from entering the secured area. A number of portals (e.g., doors, windows, etc.) may be provided around the periphery of the secured area to allow entry into or egress from the secured area.
The doors allowing entrance into the secured area, in turn, may be controlled by a card reader and electric lock that together restrict access through the portal to authorized persons. Each time a card is swiped through the card reader, the reader reads a user identifier from the card and allows access if the identity on the card matches a reference identifier.
While such systems work well, the identification cards used in such systems can be lost or stolen. Accordingly, a need exists for methods of detecting the unauthorized use of such cards.